The Switch (an Underfell - Real World fic)
by thedemonthatwas
Summary: When the only thing you have is family, what do you do? Sans learns this the hard way as he becomes a part of the real world. A world where Underfell is just a fantasy of a game on a screen. The only problem? He accidentally replaced someone else in the process.
1. TAGS AND WARNING!

_**Underfell AU/Real world Crossover fic**_

 **CHARACTERS:**

UF Sans; UF Papyrus; UF Alpyhs; UF Grillby; other/random Underfell characters

Poppy (me); Sans (my brother); Gaster (is a dad but represents my mom); other/random exaggerated characters

 **WARNING: This story contains strong language, mentions of r***, violent abuse, sexual implications, and other sensitive areas. Please do not continue if you are not fine with these things. I will add what each chapter includes at the top of each chapter.**

 **/No Fontcest: Just sibling love\**

UF!Sans/acts tough; asshole (half the time); rude; loves puns; slightly tsundere; defends his brother despite everything; I tried to keep him as close to the original as possible without seeming too OOC, so that's basically him

UF!Papyrus/abusive; violent; protective of Sans; also an asshole; slightly tsundere; angered-easily; loves puzzles, especially deadly ones; better cook than classic Papy; as close to the original UF!Pap as I could get

Poppy(me)/violent; assertive; very, very short fuse; extremely protective of her brother; insecure; acts egotistical; used to love art and sketching; great cook; blames herself for her brother's weakness; tries to make him stronger; wishes her world wasn't full of drug addicts and sociopaths

Sans(my brother)/lazy; submissive to only his sister; acts above others to feel like he's worth something; supports his sister in her endeavors; depressed; used to love programming and technology; used to love the violin; can't live without his favorite stuffed pillow; wishes he could be stronger; wishes his sister would love him more

* * *

 **/Quick Disclaimer\**

All characters based on my life are _extremely_ exaggerated. My life and relationship with my brother are not nearly as bad as this story will portray. I pick on my brother, yes. I've hurt him on purpose and on accident, yes. Like Sans, he's powerful when he needs to be, yes. But our family dynamic is not bad. This is a theoretical universe where the smallest detail is increased tenfold for dramatic effect.

Please don't take my portrayal seriously.

This is also my first dark fic. So I'm sorry if it's not too good XD

That being said, I hope you enjoy this trash little crossover fic


	2. Chapter One: Underfell

**_Disclaimer: Undertale belongs to Toby Fox, and Underfell belongs to the AU community._**

 ** _Warning: This chapter contains_** ** _genocidal death, mild abuse,_** ** _and lots of cursing_**

* * *

Chapter One: Underfell

 _Everything was dark and cold. The air around Sans pricked at his bones as he wandered around this seemingly endless void. The world around him was nothing but shadows, and he found himself getting more lost with every step._

 _._

 _._

 _._

What kind of bullshit endless place is this? _Sans thought to himself._

 _He glanced around him. To his left, darkness. To his right, darkness. Above him, darkness. His eye sockets were blank with irritation; his face portraying his extreme annoyance._

 _He paused for a moment, contemplating what he should do. Sans had noticed a while ago that there were no visible exits._

 _"Hey!" he decided to shout._

 _No answer..._

 _"This better not be some stupid idea of a joke!"_

 _._

 _._

 _._

 _"Because if it is I swear to Asgore I will find and murder your ass!"_

 _._

 _._

 _._

 ** _But nobody came..._**

 _Sans looked around again. He half expected some idiot monster to jump out and try to kill him. Hell, it wouldn't be the first time. Everyone in the Underground knew Sans only had 1 HP. A weak, 1 HP, runt monster. And yet, he was still alive. Papyrus made sure of that, after all._

 _He didn't have much more time to think about it though, as directly in front of him a faint light started to glow. Out of pure instinct, Sans started towards the light, and it steadily grew larger as he did._

 _"This better not be some sort of trap..." he mumbled to himself as the light soon became blinding, enveloping him in the white shine._

 _Sans blinked rapidly as his eye sockets adjusted to the change in luminescence. Noticing his surroundings, he soon realized he was standing in Snowdin Forest. The dark trees stood on either side of the short skeleton, and the snow glistened around his feet and flurried down from the "sky"._

 _"What..." Sans mumbled. "I...I recognize this path...?"_

 _"SANS!" a loud, demanding voice shouted from behind him._

 _He tensed and turned around to see Papyrus standing there, arms crossed with a scowl covering his face._

 _"Oh uh...h-heya boss," Sans chuckled nervously. "I wasn't slacking off I swear-"_

 _"You're so useless," the taller skeleton snapped, cutting him off._

 _"Wh-What...?" he asked in confusion._

 _Papyrus scoffed, unfolding his arms; his sharp teeth smirking ever so slightly. "You couldn't even do your job. No matter..."_

 _He turned around and started to walk in the opposite direction of Sans; his blood red scarf blowing in the wind behind him. "I shouldn't expect something from nothing anyway..."_

 _"W-Wait! Boss!" Sans stammered and started to run after him. Only just before he could reach him, the familiar sound of a knife slicing through the air resonated in his skull._

 _Sans' eye sockets widened as the human sliced his brother's head clean off. Papyrus crumbled to dust soon after. Sans froze in place._

 _"No no no no no...Not again...Asgore DAMMIT!" Sans yelled out to no one and fell to his knees by his brother's scarf, which now lay uselessly in the snow without a host._

 _Tears welled in his eyes as he stared at the piece of fabric just lying there. Why...why does this keep happening...why can't things just be..._

 _"Peaceful, Sansy?" a voice hissed from behind him as pain suddenly erupted from his chest._

 _Sans choked on a scream as blood spurted from his mouth. His sockets widened and his pupils dilated as blood poured from his chest where the knife had impaled his very soul. Which hung impaled midair on the very end of the dagger._

 _"You can only **dream**."_

 _It shattered..._

* * *

Sans screamed with and took a strong gasp for air as he jolted awake in his bed. Sweat covered his skull and had soaked his shirt rather thoroughly. Parts of it stuck to his bone as he panted in shock.

"SANS!" a loud yell came from down the hall, only muffled by the door of his bedroom and his walls.

 _Shit...What time is it...?_

He glanced over at the clock on his wall. 4:34.

Either Papyrus was already awake, or he just woke him up. Sans prayed it wasn't the latter. If that was the case, he would most likely be skipping breakfast again this morning, as well as taking quite the beating from his younger brother...

The door to his bedroom was suddenly attacked by a strong kick to the wood. The door tore right off the hinges and landed on the ground by the foot of his bed. The force of the kick was also strong enough to knock his clock right off the wall and fall to the ground.

"SANS?!"

"Holy SHIT Boss what THE FUCK?!" Sans shouted as he subconsciously pulled his sheets closer to defend himself from...whatever the fuck that was.

"Don't "what the fuck" me you lazy piece of garbage!" the taller skeleton snapped and stormed into Sans' room. "You're the one who screamed!"

Sans had barely a few seconds to bring himself back together before Papyrus had him pinned to his wall by his neck. He noted though that Papyrus was half dressed in his work clothes. His scarf hung loosely around his neck, and the bottom half of his "battle body" was finished being prepared. His gloves were also on, as Sans could feel them clutching his "throat". That was a good sign that there was a better chance of him not being murdered today...

"Ack-! I-I'm sorry, Boss! *cough* Won't happen again, I-I swear!" Sans choked out between gasps. His hands clawed and grabbed at Papyrus' arm, trying to get him to let go.

The younger brother snarled and waited before deciding to drop Sans onto the ground. He coughed several times as his metaphorical lungs were reexposed to air. Had he not been coughing or recollecting himself, Sans would have probably noticed that Papyrus had been worried. For a split second right when he broke the door down, he had been worried. Not that either skeleton noticed. Sans was fine, so there was no problem, right?

Papyrus very quickly brushed off any feeling of worry he might have had and stood straight, glowering down at his pathetic brother. "Well, at least you're awake before five this time you lazy bones! Get up, get dressed, and get downstairs! And don't make me drag you down there myself!"

With that, Papyrus stormed back out of his room and back to his own to finish getting dressed. Sans stood back up; his golden tooth glinting as his iconic grin formed the closest it could to a scowl.

He marched over to his dresser and yanked out his clothes. Anger fueled his actions as his left eye glowed a bright crimson.

 _Who the fuck does he think he is?!_

Sans threw off his soaked t-shirt.

 _Thinking he can just parade around like some paparazzi..._

He pulled on a clean new white one before pulling over his favorite red turtleneck sweater.

 _That arrogant ass..._

His thick black jacket went on last, and he stuffed his hands in its pockets. He kept on his current shorts, which were black with a yellow stripe going down each side. Exiting his room was no problem at least. After all, there was just a huge gaping hole where his door used to be.

Sans sighed silently before heading downstairs and entered the kitchen.

4:55.

Papyrus was in the kitchen and had already set breakfast on the table. Spaghetti. No surprise there.

"Hmph. Good. I didn't have to retrieve your ass," Papyrus snarled as ate.

Sans sat down and started eating as well. "It wasn't difficult. After all, I don't exactly have a fucking door anymore."

"Watch your tone you lazy bones!" Papyrus growled, his own eye sockets glowing purple.

"Why's that, Boss? I think my tone's just a-door-able," Sans sneered as he took several more bites of the breakfast spaghetti.

"SANS I SWEAR TO ASGORE!"

"You mean As-door," Sans grinned as Papyrus' eyes started to glow brighter.

"DO NOT SPEAK OF THE KING LIKE THAT YOU PATHETIC PIECE OF TRASH!" Papyrus shouted and stood swiftly, slamming his hands down on the table.

"Ah, sorry, Boss," he grinned wider. "I thought it was pretty 'humerus'."

"GAH YOU ARE INSUFFERABLE!" the taller skeleton roared and looked like he was about to flip the table and kill his own brother.

Sans smirked and did his best not to start laughing at his boss. If he did, he'd very likely be dead in the next few seconds.

"I guess I'll just head out onto my shift then, Boss," Sans stood, his grin getting wider by the second.

"SANS YOU MOTHER FUCKING-"

 _Pssssh-_

The older brother disappeared from thin air, leaving nothing but barely noticeable small red particles behind. He reappeared at his post and slumped against the wood. Sans exhaled; his breath frosting in the cold air of Snowdin.

 _Fuck you too, dear brother._


End file.
